Aug 14, 2017

Familial Alzheimer’s Disease: What You Need to Know About the Genetics of Dementia

Dementia is a complex condition that is yet to be fully understood. A vast amount of research goes into seeing what causes dementia symptoms and to see whether they can be stopped, reversed or prevented.  

There are many risk factors that can contribute to developing dementia – from lifestyle to genetics.

People affected by dementia are often concerned about whether the condition can be inherited. The genetics of dementia are complex and not yet fully understood.

Dementia can be so common, that though multiple members of the one family have the condition and there is still not a genetic link.

Though majority of dementia diagnoses are not inherited, there are some forms that are due to a genetic mutation that passes down the family line.

One such condition is Familial Alzheimer’s disease, which usually affect people under the 65 with symptoms appearing for some people in their 30s or 40s.

It’s believed that the mutated genes that causes this form of dementia play a role in the production and breakdown of amyloid – a protein that builds up in the brains of people with Alzheimer’s disease.

On average, half of the children of a person with familial Alzheimer’s disease will inherit the “faulty” gene. All those who inherit it will develop Alzheimer’s disease, and those who do not inherit the faulty gene will not subsequently pass it on to their children.

Genetic testing can identify the presence of gene mutations, as well as help determine if a person with dementia has familial Alzheimer’s, or if a child has inherited the changed gene from a parent and will develop the disease in the future.

However, genetic testing cannot determine when the symptoms will begin, though usually the age of onset is similar family members who have to condition.

When given the option to have genetic testing, some family members want to know for sure if they will later developing the condition, while others would rather not have the test as they feel they would be “burdened” in knowing their fate.


Sporadic Alzheimer’s disease

There are two kinds of Alzheimer’s disease, Familial Alzheimer’s disease, which is extremely rare, and sporadic Alzheimer’s disease.

Sporadic Alzheimer’s disease can affect adults at any age, but usually occurs after age 65 and is the most common form of Alzheimer’s disease.

Many genetic and environmental factors combine to alter a person’s risk of developing Alzheimer’s disease.

According to Alzheimer’s Australia, having a close family member with the condition increases risk – but only by a small amount.

There are certain genes in dementia research known as “susceptibility genes” which partly explain this increased risk – predominantly the apolipoprotein E (ApoE) gene. Currently there are ten identified susceptibility genes that increase the risk of Alzheimer’s disease.

However, having one or two copies of the gene increases the chance of developing Alzheimer’s disease, but does not make it certain. Some people with apolipoprotein E gene never develop Alzheimer’s, and others who develop Alzheimer’s do not have the susceptibility gene.  

Having the ApoE4 gene has been associated with increased risk for cardiovascular disease, vascular dementia and Lewy body disease.

However, it should be noted that vascular dementia and Lewy body disease are very rarely inherited from family members.

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Disclaimer: Please be aware the above article is merely information – not advice. If users need medical advice, they should consult a doctor or other healthcare professional.

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